It has been recently known that motor control apparatuses control a current feed to a motor and the rotational direction of the motor by operating switches in an H-bridge circuit. For example, the Patent Document 1 discloses a control apparatus for controlling a DC motor to be used in an electric power steering apparatus in that two semiconductor switching elements are connected in series at a current feeding line such that parasitic diodes face opposite to each other
The Patent Document 1 discloses an initial fault diagnostic sequence to be executed after an ignition power source is turned on. With regard to the fault diagnosis, when a short-circuit fault is diagnosed in a current feeding line switch, upper arm switches in the H-bridge circuit are turned on one by one to determines a detection voltage for each of two current feeding line switches. With regard to the fault diagnosis, when lower arm switches constituting a pair have a short-circuit fault, a high potential line and a low potential line are connected in a short circuit at the time of turning on the upper arm switches, and hence an overcurrent flows to cause a damage on the switches.
Additionally, at the time of determining the detection voltage, it is necessary for the initial fault diagnostic sequence to wait until the voltage gets stable after turning on or off switches. With regard to the prior art described in the Patent Document 1, it is necessary to determine the detection voltage twice for the current feeding line switches one by one with only the short-circuit fault diagnosis on the current feeding line switches. Hence, it will take longer time to carry out the fault diagnosis.
[Patent Document 1] Japanese Unexamined Patent Application Publication No. 2010-47096